Deontic reasoning is the understanding of what may, must, or ought (not) to be done under given circumstances (Wellman & Miller, 2008). Deontic logic is often applied to social‐conventional rules (such as "set the table with the fork on the left") to give those social‐ conventions moral force, even though most people would agree that arbitrary social conventions are morally neutral. A critical question concerns whether the connection between social‐conventions and deontic logic is present in young children, or learned more slowly over time. To examine this, we provided forty‐eight (24 male; 24 female) 3‐year‐ old children with an arbitrary rule for a game involving yellow and orange balls. For half the children the rule was provided with deontic language (e.g., "you should use the orange balls"), and half were not (e.g., "use the orange balls"). Additionally, half the children were given a social‐ conventional rationale (e.g., "everyone does it that way"), while the other half were given a moral rationale (e.g., "it's the right thing to do"). If children understand that deontic logic applies even to social‐ conventional rules, then we expect that they will comply with the arbitrary game rule most when the rule is provided with deontic language and a moral rationale. This research will help parents and early childhood caregivers to better understand how young children view social‐conventional rules. This in turn will provide insight into how these social conventional rules, which are highly valued and critical to learn, might best be taught within families, day cares, and classrooms.